Freeciv

The header for "Poison City"'s action performer doesn't mention a "Check for basic success." My current interpretation of http://home.tiscali.cz:8080/~cz045662/civ2/dipspy.htm says that civ2 didn't have an action failed dice roll. I therefore assume that its absence was intentional.

Backwards compatibility: Just use Action_Odds_Pct to modify the chance to become 100% (Min diplchance is 30) Do the same for all rulesetst in the initial implementation. Then change the rule (for all non civ2 rulesets?) in a separate issue by removing the compat effect.

Would require that the action probability code for "Poison City" starts to consider the success dice roll. I would prefer if this could wait until general functions for action probability with dipl combat and a failed dice roll are done. A friend of mine is working on action probability. If she doesn't get to creating general functions for action probability of actions with diplomatic combat and a success dice roll before the 3.1 data file format freeze I'll create them myself and then do this issue. (It isn't hard to implement. I would prefer that she does it. I put this task on a "ladder" of tasks that will help her learn the action probability sub system.)